Field of the Invention
The present invention relates to a photoelectric conversion apparatus, a method of driving the photoelectric conversion apparatus, a focus detection sensor, and an imaging system.
Description of the Related Art
Some imaging systems such as cameras include a focus detection sensor, such as an auto-focusing (AF) sensor. AF sensors in imaging systems are required to be capable of focusing in a diversity of scenes. Demands for the higher number of focusing points in AF sensors are therefore increasing.
A method of increasing the number of focusing points can be found in Japanese Patent Application Laid-Open No. 2013-30913, which describes a photoelectric conversion apparatus employing an area-type configuration in which linear sensors forming focusing points are arranged in a plurality of parallel lines and are connected in a column direction by common wiring. In Japanese Patent Application Laid-Open No. 2013-30913, an improvement in linearity and sensitivity uniformness is aimed by employing a non-inverting amplifier, typically, a source follower, in a readout circuit for a censor cell unit configured to output a pixel signal, and a memory cell unit configured to hold the pixel signal. The signal-to-noise ratio (S/N ratio) is also improved in Japanese Patent Application Laid-Open No. 2013-30913 by using a noise clamp circuit (transfer unit) to feedback part of noise generated in the sensor cell unit and thereby reduce the noise component of an optical signal that is output.